“Inverted tooth chains” also known as “silent chains” and mating sprockets for same are widely known and used. Conventional silent chains typically include both guide links and inverted tooth or “inside” links. The guide links are positioned on the outside edges of alternate sets of inverted tooth links. The guide links typically act to position the chain axially on the sprocket and they do not mesh with the sprocket teeth. The inverted tooth (inside) links provide the transfer of power between the chain and sprocket. Each inverted tooth link typically includes a pair of apertures and a pair of depending toes or teeth. Each toe is defined by an inside flank and an outside flank. The inside flanks are joined at the crotch of the link. The inverted tooth links are typically designed so that the links contact the sprocket teeth to transfer power between the chain assembly and the sprocket. The inverted tooth links contact the sprocket teeth along their inside link flanks or their outside link flanks or combinations of both flanks.
A conventional inverted tooth chain drive is comprised of an endless chain wrapped about at least two sprockets supported by shafts. Rotation of a drive sprocket causes power transmission through the chain and consequent movement of a driven sprocket. In a typical engine timing drive application, the drive sprocket is mounted on the engine crankshaft and the driven sprocket mounted on the camshaft.
Noise is associated with these inverted tooth chain drives. Noise is generated by, among other things, the impact sound generated by the collision of the chain and the sprocket at the onset of meshing. The loudness of the impact sound is affected by the impact velocity between the chain and the sprocket and the mass of chain links contacting the sprocket teeth. Another cause of noise is the chordal action of the chain. Chordal action occurs as a chain link encounters the sprocket from the free span. The meshing of the chain and sprocket at the chain mesh frequency can cause a movement of the free span in a direction perpendicular to the chain travel but in the same plane as the chain and sprockets. This vibratory movement can also produce an objectionable sonic tone.
Many efforts have been made to decrease the noise level associated with inverted tooth chain drives. The problem of noise reduction was addressed in U.S. Pat. No. 4,342,560 by changing the contacts between the link flanks of a silent chain and the sprocket teeth by having differently configured link flanks in different sets of the chain to alter the point and rhythm of contacts. A similar concept was used in U.S. Pat. No. 4,832,668. Each of these patents teaches the reduction of chain noise level by randomization of elements within the chain, such as link configuration or profile, or link aperture-to-flank spacing distance.
U.S. Pat. No. 4,915,675 utilized the same concept of modifying the pattern of sound emanating from the chain by altering the types of link configurations. That patent teaches the utilization of an asymmetrically shaped link which is then oriented in two different directions in the chain assembly to alter the point and rhythm of chain to sprocket contacts.
Other attempts to alter the rhythm of contacts between the chain and sprocket have focused on the modification of elements within the sprocket, such as the sprocket tooth profile or the spacing of the sprocket teeth on the sprocket. For example, U.S. Pat. Nos. 3,377,875 and 3,495,468, teach modification of certain sprocket teeth or even elimination of some teeth in order to achieve noise reduction in contacts between the links of the silent chain and the sprocket teeth.
Other noise reduction attempts include efforts to modify sound patterns by various phasing relationships between the chain assembly and the sprockets. Phasing the chain and sprocket relationship can reduce the number of chain link teeth (or mass of chain) impacting the sprocket during a given time increment. Similarly, phasing the chain and sprocket relationship can alter or phase the chordal action or articulation of the chain and sprocket. Both of these phasing modifications, alone and in conjunction with the randomization of the chain and sprocket contacts, can alter the impact and chordal action generated sound patterns.